Believe in power of prayer. Will it work for overactive bladder?

It Depends. If you are speaking of faith healing in general, as a physician and scientist, I cannot vouch for that as a viable medical intervention. However, since overactive bladder is a condition highly affected by stress and other goings-on in your brain, I would not dispute that stress-reduction by any means or any activities that contribute to positive thinking and overall feeling of well-being can help.